Corona elimination in generator end windings



Feb. 17, 1948. s, JOHNSON 2,436,306

CORONA-ELIMINATION IN GENERATOR END-WINDING Filed June 16, 1945 WITNESSES: INVENTOR Jf/ fa/$77 5. 106273017.

ATTORNEY Patented Feb. 17, 1948 CORONA ELIMINATION IN GENERATOR END WINDIN John S. Johnson, Wilkinsburg, PL, asslgnor to Westinghouse Electric Corporation, East Pittaburgh, Pa., a corporation of Pennsylvania Application June 18, 1945, Serial No. 599,834

4 Claims. (Cl. 174-43) My invention relates to a high-voltage apparatus which comprises a plurality of closely spaced insulated conductors which are subject, at times, to such high voltage-difierences between them, that corona-preventive measures are necessary. While my invention is of more generic applicability, it was specifically designed for crossconnecting the semiconducting corona-preventive surfaces of certain insulated conductors of the end-windings of high-voltage dynamo-electric machines such as synchronous generators. Although it is generally applicable to all of the spaced conductors of the end-windings of such a machine, my invention finds its greatest applicability, at present, to the provision of semi-conducting cross-connections at the junction of different phase-groups, or between layers of conductors which have unusually high voltage-differences between them, as compared to other pairs of conductors of the end-windings.

In high-voltage machines of the type to which my invention applies, the severa1 conductors have each been covered by insulating inner layers, and at least the outer exposed portions of said insulating layers have been covered by semiconducting outer layers, usually provided by a semiconducting paint or compound. In the past, semiconducting spacing-blocks have been utilized between the treated conductors which are subject, at times, to such high-voltage differences between them that corona-preventive measures are necessary. In the past, these semiconducting spacing-blocks have been substantially non-resilient, and they have necessitated roping in place,

' with a semiconducting glass twine, to hold them in place in the event that they should loosen in service.

The twine has not always maintained a sufli- 1 ciently firm contact between the spacer-blocks and the treated surfaces of the conductors between which the blocks were placed, sometimes resulting in visible corona appearing at these points of contact, thus not only defeating the purposeof the corona-preventive treatment, but also being destructive to the semiconducting ma terials. Furthermore, the semiconducting twine has caused difliculty, because it, in effect, shortens the air gap between adjacent coils or spaced conductors, because the semiconducting twine takes up some of the space, and thus the twine sometimes results in the formation of visible corona at the points where the twine comes closest to the next adjacent spaced conductor, in spite of the corona-preventive treatment. This condition is aggravated, because of the fibrous nature of the twine, which results in a rough surface, with many fine protruding filaments, each one or which becomes a point of high voltagestress concentration.

An object of the present invention is to overcome the foregoing and other difliculties by utilizing, at least for the places where the highest voltage-stresses are encountered, compressible resilient semiconducting blocks, which are held in compression between the treated surfaces of the conductors in question, and which hold themselves in place, by their own resilience, without requiring any roping.

With the foregoing and other objects in view, my invention consists in the combinations, parts, apparatus, and methods hereinafter described and claimed, and illustrated in the accompanying drawing, wherein Figure 1 is a perspective view of a portion of the end-windings of the stator'member of a highvoltage synchronous generator to which my invention is applied, parts being broken away in section, to show the construction;

Figs. 2 and 8 are perspective views of two of the forms which my resilient spacer-blocks may take; and

Fig. 4 is a perspective view of a clamping-tool .which may be used to insert my resilient blocks.

In the application of my invention which is illustrated in Figure 1, the primary winding 3 of a high-voltage polyphase synchronous generator 4 is mounted on the stator member 5 of the generator, For clearness in illustration, the rotor member is not shown, The stator member 5 comprises a stator core 6 of a type having a smooth cylindrical bore, and having conductorreceiving slots 1 for receiving the high-voltage polyphase winding 3. This winding has coil-sides 8, lying in the slots 1, and it has an end-winding portion 9 which consists of spaced insulated conductors I I, which have gaseous spaces between them, and which are subject, at least at times, to

- such high voitage-diflerences between them, that corona-preventive measures are necessary. Each conductor H. as exaggeratedly indicated in Fig. 1, comprises a strap-conductor [2, which is covered by an insulating inner layer I3, which is in turn covered by a semi-conducting outer layer I4 which may be provided by a semi-conducting compound, or by other means, as is well known in previously used corona-preventing means for such machines.

These spaced end-winding conductors H, or at least the pairs of conductors between which the voltage-diiference is not too excessive, may be or layer.

braced. in a known w, by nibstantiaily nonyielding spacers II which are roped in place y twine II. The non-yielding spacers II and the twine I! may, or may not, be impresnated with semiconducting material, but preferably. in either event, they are coated with a semiconducting painted coating.

Between the spaced conductors of different coil-groups, or between diifrent phases. or be-' tween any other two spaced conductors where the voltage-gradient isexceptionally large, endangering the formation of corona, I prefento apply my new compressible resilient semiconducting spacer-blocks 2|. the use'of which may be confined to these places of exceptional voltage-stress, as indicated in Pig, 1, or the semiconductingi-esilient spacer-blocks It may be utilized throughout,- to the exclusion of the rigid or non-yielding spacers ll, if desired. The resilireadily solved.

- I claim as my invention:

1. A high-voltage electric apparatus compris- I ,ing a plurality of closely spaced insulated conent blocks 2| are composed of a rubber-like material, which ispreferably one of the new synthetic materials, such as the silicon rubbers, having a far greater heat-resistivity than natural rubber. This, rubber-like material is preferably loaded witha semiconducting material such as carbon or reduced titanium oxide, or its semiconducting quality may be given to it by means of an externally applied-semiconducting coating The thicknessoLthe rubber-like spacer-blocks 2| is such that each resilient block is compressed when it, is in place between the two spaced conductors Ii with which it is associated.

The use of this type of spacer 2| results in an intimate contact between the spacer and the treated surfaces of the conductors, thereby eliminating the possibility of corona forming as a result of imperfect spacer-contact. Also. because of the rubber-like nature of=-the material, and because itis under compression, my new spacer 2| will stay in place without roping. By this, I mean that the many turns of strong twine, which have heretofore been utilized with non-resilient spacers such as ii. are not needed.

The shape of the resilient spacer 2! may be either flat, as shown inFlg. 2, or of a shaped or molded section. preferably of such configuration that the uncompressed spacer-block 2i approximately fits partiallyaround the surfaces between which said block iscompressed. One of the conilgurations which the spacer-block -21 may assume is shown at ii in Fig. 3. In this way, the shape of the spacer causes it to have a sort of interlocking action which helps to hold it inplace.

The use of a rubber-like material for the spacer 2| makes the application of the spacers a more economical manufacturing operation, saving the labor-cost which is involved in roping the non-resilient spacers of the :previous practice.

The resilient spacers ii can be applied, after the still end-winding'condlictors II are in place in the machine, by first compressing each spacer 2 I, as indicated by the .clampl' z-blades I in Fig.

4, then inserting the spa er between the conductor-pair in question, and removing the clamping-tool by withdrawing the blades 28, leaving the spacer in place, where its own resilience holds itin place; 7

Because of the complex nature of the endwindings 9, it is not always possibleto complete .ly anticipate the number and the of all ductors, said conductors having gaseous spaces between them, and being subject, at times, to such high voltage-difierences between them that corona-preventive measures are necessary. said conductors being covered by insulating inner layers, and at least the outer exposed portions of said insulating layers being covered by semiconducting outer layers, in combination with one or more compressible resilient semiconducting blocks held in compression between the semiconducting outer layers of one or more pairs of such conductors and held in place bytheir own resiiience.

2. The invention as defined in claim 1, characterized by said block or blocks having an initial uncompressed conflguration adapted to ap-; proximately fit partially around the semiconducting surfaces between which said block or blocks are compressed.

3. The invention as defined in claim 1, characterized by said block orblocks being composed of a rubber-like material loaded with a semiconducting material.

4. A high-voltage electric apparatus comprising a plurality of closely spaced insulated conductors, said conductors having gaseous spaces between them, and being subject, at times, to such high voltage-difierences between them that corona-preventive measures are necessarmsaid conductors being covered by insulating inner lay- 111' r Q e0 thispatent ers, and at least the outer .exposedportions of said insulating layers being covered by semiconducting outer layers, in combination with a semi-.

" conducting connecting-block, between the semiconducting outer layers of one or more pairs of such conductors, the opposite faces ofsaid semiconducting connecting-block comprising resilient semiconducting material held in compression against, and making an intimate electrical contact with, the semiconducting outer layer of oneof said .conductors.

JOHN S. JOHNSON-.-

' REFERENCES The following references are of record in the UNITED STATES PATENTS Date Number Name 2,042,208 Calvert May 26, 1936 2,318,074 Hill et al. May 4, 1943 2,331,098 White et al Oct. 5, 1943 2,390.905 Wening et al. Dec. 11, 1945 

